1. Field
The present invention relates to a method for ensuring the internal tightness of elevator hoisting ropes and to elevators permitting the use of the method.
2. Description of Related Art
In the use of hoisting ropes, and especially thin elevator hoisting ropes provided with a steel core, it is important to make sure that the mutual tightness of the strands of the hoisting rope is correct after installation and remains as correct as possible during operation of the elevator. The internal tension of the rope may change during installation of the elevator in connection with the handling of the rope. Any loosening between the strands that has started at installation time may accumulate in a given portion of the rope in the longitudinal direction of the rope during operation of the elevator. Such a portion may be e.g. the stretch between the traction sheave and the suspension point in the ceiling if the originally loosened part was in this rope portion. When the rope is twisted in the loosening direction relative to its braid structure, the braiding of the strands forming the rope sheath is opened and the braid structure holding the rope in shape becomes loose, with the result that the interlock between strands is loosened and the contact of the strands with each other is diminished. In consequence, the length of the rope sheath, i.e. the outermost layer of the rope, is increased along the length of the rope, and so the load of the rope is shifted to the straight core strand. Such internal loosening of the rope is a definite risk factor, which may cause serious damage to the hoisting rope.